The long-range objective of this project is to understand the mechanism(s) by which human choriogonadotropin (hCG) stimulates steroid production in its target cells. Using a clonal strain of cultured Leydig tumor cells, the following phenomena are currently being investigated: 1) fate of the receptor-bound hormone and its relation to the expression of biological activity; 2) regulation of gonadotropin receptors and steroidogenic responses by homologous and heterologous hormones; and 3) regulation of steroidogenic responses by substrate availability.